When crews arrived, they said smoke was pouring from the eaves around the building and the attic was filled with smoke.

An initial investigation suggests that the intense heat from the facility's incinerators sparked the fire.

"The crematorium operates at about 1700 degrees," Merrimack Fire Chief Mike Currier said. "They are saying it's at its max because of what they're doing, and the radiant heat from the exhaust itself caught the rafters and roof on fire."

Crews were able to knock down the flames, but one firefighter was transported to the hospital with injuries described as lacerations.